Universal Mobile Telecommunications System (UMTS) is a third-generation (3G) wireless communication technology. The radio access network of UMTS, the UMTS Terrestrial Radio Access Network (UTRAN), provides wireless connectivity for both circuit-switched and packet-switched traffic between User Equipment (UE) and the core network, via Radio Network Controllers (RNC). Each RNC controls one or more Base Stations (BS), which provide the air interface connectivity to mobile UEs. Wideband Code Division Multiple Access (WCDMA) is one technology employed in UTRAN implementation.
High-Speed Downlink Packet Access (HSDPA) is a mobile telephony communications protocol for delivering packet data at high transfer speed and capacity. Downlink channels (i.e., transferring data from BS to UE) in the HSPDA protocol lack the variable spreading factor and fast power control of traditional CDMA, and instead use adaptive modulation and coding, fast packet scheduling at the BS, and transmit at full residual power. Hybrid Automatic Repeat-Request (HARQ) is employed for fast retransmission of corrupted packets. In particular, HSDPA in WCDMA is supported by a physical control channel, high speed shared control channel (HS-SCCH), and a high-speed physical downlink shared channel, (HS-PDSCH).
Release 7 of the UTRAN specification defines “continuous connectivity for packet data users,” or simply, Continuous Packet Connectivity (CPC). The original objective of CPC was to enhance system capacity to support a very large number of packet-oriented users by reducing signaling overhead and uplink interference. This would make it possible to keep many packet data users in the CELL_DCH state for long time periods, without reducing the cell throughput. These packet data users would experience significantly reduced delays as time-consuming reconnections are avoided, providing a user experience similar to fixed broadband.
The objective of CPC has expanded and now includes reduction of the downlink overhead and reduction of the user equipment (UE) power consumption. The CPC solution includes a new uplink dedicated physical control channel (DPCCH) slot format, discontinuous uplink transmission, discontinuous downlink reception and HS-SCCH-less operation.
The HS-SCCH-less operation is intended for low data rate users such as voice over IP (VoIP). The goal is to reduce transmission of downlink HS-SCCH, which would generate a significant amount of overhead for small data packets, by only transmitting the HS-SCCH during retransmissions (maximum two retransmissions). Since the HS-SCCH normally precedes data transmission on the HS-PDSCH and includes information such as the transport format, in CPC mode UE must employ blind decoding among four predefined block sizes. The new feature is supported by a new CRC computation method (Type 2) for the HS-DSCH and a new HS-SCCH format (Type 2). The UE should also be capable of receiving and decoding transmission according to the legacy (Rel-6) HSDPA formats, referred to as Type 1.
HS-SCCH-less operation is configured by the serving radio network controller (SRNC) per UE, by prescribing up to four transport block sizes using up to two HS-PDSCH codes. A UE should still be able to monitor up to four HS-SCCH transmissions (Type 1 and Type 2) and should also be able to detect if a received HS-SCCH transmission is of Type 1 or Type 2. Additionally, a UE should decode up to two HS-PDSCH transmissions of Type 2. Retransmissions should use the same HS-SCCH type and HS-PDSCH type (Type 1 or Type 2) as in the first transmission.
In the HS-SCCH-less mode, the first transmission is not signaled via the HS-SCCH. Instead, the UE must demodulate the symbols on 1 or 2 predetermined HS-PDSCH codes and perform blind decoding of the received symbols. There are four possible transport formats. The UE should perform rate matching corresponding to each of the formats to decode the resulting sequence, and check the CRC that is masked with the UE ID. If the CRC check on a candidate sequence is successful, the sequence is accepted by the UE and an ACK is sent to the BS. If the blind detection of the first transmission is unsuccessful, the BS will signal the subsequent retransmission using the Type 2 HS-SCCH. The Type 2 HS-SCCH transmission thus precedes the second and third HS-PDSCH transmissions in HS-SCCH-less operation.
Part one comprises, as in Release-6,                channelization code set (7 bits)                    only values corresponding to one and two codes                        modulation index (1 bit);                    ‘0’ indicating QPSK                        
Part two is modified in Release-7, and comprises                special information type (6 bits)                    ‘111110’ indicating HS-SCCH less operation. Note that the first six bits of part 2 in REl-6 HS-SCCH is the transport block size. The value ‘111110’ would correspond to a very high code rate that would not be used in practice.                        the special information (7 bits)                    transport block size (2 bits)            pointer to the previous transmission (3 bits); indicating 6-13 subframes since last transmission            second or third transmission (1 bit)            reserved bit (1 bit)                        
The redundancy version for the second transmission is three, and for the third transmission is four.
In the case that no HS-SCCH transmission is detected and HS-SCCH-less operation is activated, up to four different HS-DSCH transport formats should be blindly decoded. In addition, in HS-SCCH mode, if an HS-SCCH transmission is not detected by the UE, HS-PDSCH retransmissions must also be blind decoded. Blind decoding up to four transport formats requires significant decoding resources in the UE. By reducing the total number of blind HS-DSCH decoding operations in the UE, both the required hardware resources and power consumption may be reduced.